1. Field of the Invention
The present invention relates to method and apparatus for the representation, storage and transmission of digital data, and particularly relates to high capacity data storage and retrieval.
2. Description of the Prior Art
Conventional techniques for data storage and handling, such as punched paper cards and tape, magnetic disk and tape devices, semiconductor chips, and recently developed optical storage devices, employ a two state or binary signal known as a "bit" as the basic unit of data representation. Because of the two-stage nature of the bit, data is represented in the form of binary numbers, as it is in the main memory and central processing unit of digital computers.
To represent numerical data such as integers and real numbers, groups or bytes of 16, 32, or 64 bits are commonly formed as the fundamental storage unit. For example, a 16 bit word can represent integer numbers from -32,767 to +32,767. Text characters, like alphabetic upper and lower-case letters, are represented by standardized values of an eight bit storage unit known as the "byte".
Binary representation of digital data, although in common and widespread use, is not the most efficient utilization of storage media. Various attempts have been made to record more information within each physical storage unit of the recording medium. For example, U.S. Pat. No. 4,544,961 describes a device which magnetically records digital information using two parameters of the recording medium: the polarity of flux change in, and the length of breaks between, magnetized regions.
U.S. Pat. No. 3,969,593 discloses an optical sound recording system for use with motion picture film, in which independent sound channels may be recorded on the same track by using hue variations in superimposed, but different colors. These approaches thereby provide recording systems wherein information is stored via the variations in discretely separate, varying parameters.
Holography provides another approach to digital data recording. An overview of this technology is given in Handbook of Optical Holography (Ed. Caulfield, A. J., Academic Press Inc. 1979, Chap. 10). This storage method typically provides a set of superimposed "pages", wherein each page is a two-dimensional matrix of binary digital cells.
It is helpful to describe data recording systems in terms of recording vectors, or dimensions. In U.S. Pat. No. 4,544,961, the recording vectors, or dimensions, were the flux polarity and the spacing between magnetized regions. In U.S. Pat. No. 3,969,593, the recording vectors, or dimensions, were the two colors whose hues were varied to independently store ,the two soundtracks at the same location. As used herein the term "vector" will be used to denote a detectable variable associated with a unit of storage area on the recording medium.
In conventional binary storage systems, storage capacity is simply a linear function of bit density. In multiplexed systems, wherein more than one item of recorded information may be superimposed at a common location, storage capacity increases exponentially with the addition of each recording vector. Since each vector can reside in one of a variety of states, the representational power of each storage unit is equal to the product of the number of states in which each vector can reside, thereby yielding the exponential relationship.
The multiplexed quantization of these aforementioned systems can be characterized as non-logarithmic, in that each vector of one multiplexed storage unit can exist in one state. Therefore, just one value can be recorded on each vector of each multiplexed unit. In the '961 system, for example, the value of the recorded flux change is either positive or negative at the location of interest In the '593 system, each color has a single hue value at a given location on the film.